White roofs, streets could curb global warming

[Dover]

I recall mentioning this idea here in this forum some time ago. It did seem a little far fetched,
but no more so than some European countries covering their mountainsides with reflective foils.

Apparently it was not exactly an original idea:


The idea of painting our roofs and roads white to offset global warming is not new, but a recent study has calculated just how significantly white surfaces could impact greenhouse gas emissions. Last week, researchers at Lawrence Berkeley National Laboratory and UC Berkeley presented their study at California's annual Climate Change Research Conference in Sacramento.


If the 100 largest cities in the world replaced their dark roofs with white shingles and their asphalt-based roads with concrete or other light-colored material, it could offset 44 metric gigatons (billion tons) of greenhouse gases, the study shows. That amounts to more greenhouse gas than the entire human population emits in one year, according to a recent article in the Los Angeles Times. The strategy could also offset the growth in carbon dioxide emissions, which account for about 75% of greenhouse gases, for the next 10 years.

The reason for white is simple: white reflects the sun´s rays more than black does. The study´s coauthor, LBNL physicist Hashem Akbari, explained that it takes about 10 square meters of white roof to offset 1 metric ton of carbon dioxide. In warm climates, white roofs have the additional benefit of lowering the cost of air conditioning by up to 20% in hot months.

It´s this second reason of reduced cooling costs that prompted the state of California to require in 2005 that flat-roofed commercial buildings have white roofs. In 2009, the state will require that new and retrofitted residential and commercial, with both flat and sloped roofs, be installed with heat-reflective roofing. The requirements are part of California´s energy-efficient building code.

Globally, roofs account for about 25% of the surface of most cities, and pavement accounts for about 35%. Even without cutting industrial pollution from current levels, installing white roofs and pavements could offset more than 10 years of emissions growth, according to the conference data.


Cont'd

http://www.physorg.com/news140875649.html

--------------------------------------------


Study: white rooftops could curb climate change

If the world’s 100 biggest cities were to whiten the roofs of all of their buildings and use more reflective pavement, the global cooling effect would be huge, a new study has concluded.

Speaking at the Fifth Annual California Climate Change Research Conference in Sacramento, Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, said that he has created a formula to determine how much heat-trapping carbon dioxide would be offset by reflecting the solar radiation back into space. In his presentation , he said that replacing the dark shingles on a 1,000-square-foot roof – the average size of an American home – with white material would offset 10 metric tons of greenhouse gases.

His paper, “Global Cooling: Increasing Worldwide Urban Albedos to Offset CO2,” will be published in the journal Climatic Change.

While this may sound like greenwashing (but with whitewash), the potential savings here are huge. The LA Times walks us through the numbers...>


http://tinyurl.com/4gbrov

[Mme. Defarge]

1. I was wondering if

we could keep the oceans from warming up due to the melting of the polar ice caps by floating large, white surfaces that would reflect light. An engineering fix as part of the solution?

[DesertRat]

2. Pretty common here in Phoenix

Lots of flat white roofs.

[Gregorian]

3. There is also global dimming.

http://en.wikipedia.org/wiki/Global_dimming


Every time I see something that makes a hypothesis regarding some kind of repair to our ecosystem I have to wonder. I say that because this system is more than extremely complex. It's mysterious. So we've messed with it enough to push it out of equilibrium, and now we might try to bring it back by our own hand. I doubt it. I really doubt it.

On the positive side, there are so many other galaxies out there that ruining one planet may not be that important in the greater scheme of things. Even if it's the only one with life. I'm not so sure this organism is all that valuable after all.

:)

[susanna]

4. Makes sense to me...

ameliorates the "heat sink" phenomenon (dark roofs, streets, parking lots drawing and storing daytime sunlight to heat up the region).

[InternalDialogue]

5. I understand the reduction to the cost of air conditioning.

So that's 20 percent less air conditioning used by homeowners and business owners.

But the reflectivity? The solar energy that reflects off a surface at ground level is already inside our "greenhouse." How much of what is reflected off the surface of the earth actually makes it back outside our atmosphere?

[Dead_Parrot]

7. If it's reflected as visible light, nearly all of it

The problem with dark surfaces, like most roofs, is they absorb the visible light (which passes through the atmosphere) and re-emit the energy in infrared (which doesn't, in general). If it's bounced straight off at the same sort of frequency it came in on, on the other hand, it shouldn't have much effect.

It's a neat idea: hopefully it'll get some proper consideration.

[InternalDialogue]

8. Ah, so the key is returning the energy in the same form -- visible light.

Got it. Thanks for the response.

[meow mix]

34. thats the part i was missing too i guess..

thanks for asking =)

[Mr_Jefferson_24]

6. K&R. Some of the meaningful things that can be very...

...helpful if done by enough people are mind numbingly simple and not all that expensive.

[Liberty Belle]

9. Concrete is way, way too expensive for roads compared to asphalt.

We got a bid to do concrete on our long driveway; it was over $10,000; redoing the same thing in asphalt was about $3,000. No way can we afford to do all our highways in concrete.

White roofs may work though.

[Dead_Parrot]

11. Different scenarios, though

For your driveway, asphalt probably is the best choice - nearly all the wear and tear is down to the weather, rather than streams of trucks and buses, so there's no point is paying the extra. For public roads, the strength of concrete makes it last a lot longer and the costs tend to break even, or even lean towards concrete - I think it's hardness makes for better fuel economy, too.

[Not Sure]

32. A driveway is much different than a roadway

On one road project I'm designing, it's actually cheaper to pave with unreinforced concrete than with asphalt for the temporary turnarounds necessary at the dead-ends built at the end of each phase of the project (it's a long thoroughfare project). The change in the past year is the price of oil, which is a major component of asphalt. Granted, it's unreinforced, but it's still hand formed and poured (slipform machines are not used in this area), which is labor intensive.

In this case, the permanent roadway section is 8 inch thick concrete 25 feet wide, so an equivalent asphalt roadway is fairly substantial. Naturally, roadways like these are much more expensive than a driveway per square yard, so slight differences in unit price over the course of a large project become magnified. I suspect a large part of the cost of your driveway is the set up and reinforcement, neither of which is required for asphalt paving.

[reggie the dog]

10. I live just inland from the French cote d'azur

we have mostly pink/orange tire roofs here. Most people I know do not have air condidtioning. I have a unit that was in my apartment when I bought it. The previous owner took off the storm shutters and put in AC, the condo association made him put the shutters back in. We close out the hot sun in the summer and HAVE NEVER USED OUR AC. It gets up to the mid 90's low 100's for part of June, July August and part of September. In the winter we let the sun in to heat. I will not use the gas powerd water radiator heating we have until Novemeber. We set the temp at 18C over night and 20 during the day but once it is sunny out the sun and the double plane windows combine to heat up the place without using our heater.

[kmdemqueen]

12. That is very interesting

[OakCliffDem]

13. I wonder if the streets were reflective gold, would that help?

Then America could really be the land where the streets were paved in gold!

[kristopher]

14. No help for albedo

The average area of the Arctic ice in summer is about 2.5 million square miles, and during the winter about 6 million square miles. We soon expect the summer ice to disappear. This is of great concern to climatologists because it changes the reflectivity (albedo) of the Earth.

There are 83 million residential buildings in the US. Using an average of 1000 square feet per unit (it is actually more) that makes 83 billion square feet of RESIDENTIAL roofing.

So if we read this article, it sounds like we might be onto something to mitigate the loss of Arctic ice, right?

Not so fast.

83,000,000,000 square feet only equals about 3,000 square miles.

Now the homes are much further south than the arctic ice so there would be a large difference in how much energy is reflected per square mile, but it isn't going to even come close to equating the amount of energy reflected by the ice.

[Kolesar]

16. Your math is right

Adding commercial flat roofs ought to double the area (but it's still not much area).

Pavement area has got to be huge compared to roof area. Our driveway has about the same area as the house and garage combined. Add to that the area of roads and parking lots.

[Dead_Parrot]

17. Your math is so far out it hurts.

First off, let's head down memory lane: http://www.democraticunderground.com/discuss/duboard.php?az=show_topic&forum=115&topic_id=161146

"As of 2000 in the US residential sector alone there were about 83 million buildings with a combined square footage of roughly 170 billion square feet...."

Feel free to let us know if you were talking bollocks then, or are talking bollocks now, or just like to fudge the figures by a factor of 2 depending on what point you are trying to make.

Either way, you didn't factor in commercial buildings and you totally missed the roads, which make up the greater part of it.

You also appear to have forgotten what "globally" means - it means you include the roads and roofs where the other 96% of the population live - but at least you realised angle makes a difference.

So, if we take your low 3,000 figure and multiply by 2 (for commercial buildings, assuming Boreal is right), then 2.2 (for the roads) then 20 (for everybody else) then 4 (the increase in incidence from around 10 degrees to an average of 45) we wind up at just over a million square miles (polar ice equivalent). That's definitely a mitigation, especially if we do it while there's still some sort of ice-cap.

If we take your high figure it works out at a shade over 2.1 million square miles of ice - which is what we'll be down to in a couple of summers.

[kristopher]

18. Thanks for tracking the link down

I recalled the # of buildings but forgot the square foot number, I just recalled it was over 1000 per building - a point noted in my post. Using the link I checked the commercial floorspace, it is about 74,000,000,000 sqft.

So that gives us 170,000,000,000 + 74,000,000,000 for 244,000,000,000 sqft or about 9000 square miles. Your use of roads I completely reject as just too impractical to implement - we have no material that will withstand the wear. If we use concrete not only does it involve massive expense in both money (better spent elsewhere) and carbon emissions, the benefit would be very short lived since the drip of oil soon turns the center strips of each lane black.

Where do you get multiple of 20 for the rest of the world? I'm guessing it is basic extrapolation from population, but that would be obviously inappropriate since the US living standard in terms of per capita SQFT of living space is well above the rest of the world. In addition the commercial development elsewhere is likewise much lower than the US; therefore, using the US as a benchmark is simply not tenable.

I didn't and don't claim to have a comprehensive analysis because the difficulties of going global with such an exercise are obvious. However, considering world economic realities and technical limitations related to paved areas I don't think my first draft is very far off at all - it definitely places the scale of the benefits more accurately than the speculation you provided.

[Dead_Parrot]

19. It's not my use of roads...

...It's a basic assumption of the paper. It would have been useful to point out you rejected that in the first place, no? Then we could discuss the limitless supply of cheap ashphalt you've found instead, and how enviromentally friendly it is, and also how often it needs replacing.

20 was a thin-air figure, and you're right, it will be smaller. It's academic, of course, since the paper is talking about just 100 cities and actually gives the area as 0.38x10¹²m², or 146,720 sq miles. Wrangled through 45 degrees, that's the equivalent of around 587,000 sq miles ice. should make a difference, don't you think?

They do also discuss the actual albedo, but I'm being too lazy to compare albedos for ice vs water, and concrete or paint vs ashphalt or tile. I'm guessing they're roughly equvalent.

[kristopher]

20. The asphalt is already in place, so your argument is specious.

Replacing all of that asphalt is an absurd proposition on the face of it no matter what metric you use.

note: I see the origin of my use of 1000sqft per residence. It is from the author of the paper: "Speaking at the Fifth Annual California Climate Change Research Conference in Sacramento, Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, said that he has created a formula to determine how much heat-trapping carbon dioxide would be offset by reflecting the solar radiation back into space. In his presentation , he said that replacing the dark shingles on a 1,000-square-foot roof – the average size of an American home – with white material would offset 10 metric tons of greenhouse gases."

So there are actually two threads being discussed - individual homes and urban roofs/pavement. On the issue of urban roofs, my experience is that many urban rooftops are already light colored. A standard covering is formed with rubber sheeting covered with asphalt and then topped with light colored gravel to provide UV protection.

The basis of this article is a not so well done power point presentation that has been submitted to a journal. The author works in the well established field of island heat effect. I doubt there is little original here regarding valid suggestions for change. Rather, the hook for publication is relating some very general (and extremely hypothetical) figures on a shift in reflectivity to climate change concerns. It has very, very limited real world application.

[tinrobot]

21. Asphalt wears out, roads always need to be repaved.

When you have to repave the road, pick a lighter material.

Within 20 years, most of the asphalt would be gone.

[kristopher]

22. You have no idea what is involved; I don't believe you know anything about roads.

Repaving an asphalt with asphalt is not very difficult or energy intensive. Resurfacing an existing asphalt road with concrete is much closer to what is involved in building a road from scratch so I think your imagined savings are questionable. There is also the issue of CO2 emissions from the concrete. With asphalt the carbon is still sequestered.

Perhaps you could find a comparison of the two materials that would shed some light on the topic so that your positions are based less on 'thin air'.

In any case, the entire idea (from the view of albedo change) is nothing. There are similar proposals suggesting the benefit to be derived from globally replacing plants with shiny leaves with plants that have fuzzy leaves. Interesting, but it isn't going to happen.

[tinrobot]

30. Asphalt doesn't have to be black

You can make it just about any color.

Here's a company that does just that:

http://www.asphacolor.com/index_main.html

[Dont_Bogart_the_Pretzel]

33. Neat, I read something about this sometime ago

"Asphacolor Corporation was created in 1992 to provide an alternative to plain black asphalt."

Bermuda Green
or
Sequoia

Now every time I mow the yard(BIG), I'll think(daydream) of this.

[Dead_Parrot]

25. Yeah, until the next time they need replacing

Saying it's "already in place" is so breathtakingly shortsighted it makes me wonder why you bother reading E/E at all.

Interestingly, Public works magazine - which, if you can't guess from the title, is actually for people who undertake these projects - seem to dissagree about the level of absudity:

Four types of concrete overlays are currently in use: whitetopping, ultra-thin whitetopping (UTW), bonded overlay, and unbonded overlay. “Ultra-thin whitetopping is gaining in popularity because it can be done so easily,” said Haislip. UTW is used in situations where the existing asphalt pavement is full-depth (asphalt surface on asphalt base), and is ideal for normal traffic loads on residential streets and low-volume roads. It also can be used in asphalt intersections where pavement shoving and rutting are problematic.

I can't help but compare this with "Resurfacing an existing asphalt road with concrete is much closer to what is involved in building a road from scratch" and wonder if you actually have a clue what you're talking about at all. And yet you say to TR "I don't believe you know anything about roads".

Again, breathtaking.

I really don't know why you think swapping dark surfaces to light ones is a "hypothetical" shift in reflectivity. Do you need a dictionary, perhaps? or an eye test?

[kristopher]

26. Changing my mind

The article doesn't give a great deal of support for your proposal.


The bulk of your source has this to say. :
Cost is often the No. 1 factor that public works departments must consider, but basing assessments solely on upfront costs can be dangerous. Cost of the raw material may fluctuate daily or may be difficult to acquire locally (think of rising oil costs or shortages of portland cement). Both ACPA and NAPA encourage public works departments to look at the long-term costs of maintenance and rehabilitation when deciding which material to specify. Because estimates show that 25% of roads in cities across the United States must be either rehabilitated or completely replaced in the next two years, public works officials must take a close look at how those costs are going to affect them in the long run.

Haislip said that asphalt is more common for a department to specify than concrete. “Asphalt over concrete—that's the standard,” he said. “That's what they've been doing for so long.”

But because it's the “standard” doesn't necessarily make it the best option for all applications. Concrete may be better in some instances, the first of which is new construction. In urban metropolitan areas, where new roads are being built and existing roadways are being expanded, using concrete may be a good way to minimize future inconvenience. “Funding is a big challenge, however,” said Haislip. “People are looking for short-term fixes, which have a political impact.”

Another place to use concrete paving is where underground utilities need to be redone. When separating sewer and drainage pipes (no more combined sewers), the public works department must dig out the roadway, which could present a good opportunity to go in and place longer-life pavements.

Asphalt also can be specified as a long-term solution. “Some pavement types must be completely removed and reconstructed when they reach the end of their design life, but total removal and reconstruction due to structural failure of a thick asphalt pavement is rare,” said Margaret Cervarich, vice president of marketing and public affairs with NAPA. “With a thick asphalt structure, it is possible to obtain a ‘Perpetual Pavement,'one that can last indefinitely, with the only rehabilitation being milling of the surface followed by an asphalt overlay.” Perpetual Pavement is a relatively new type of asphalt concrete pavement designed to resist structural fatigue distress for at least 50 years. Maintenance is limited to replacement of the surface course.

[Dead_Parrot]

27. Right, so...

...you bold the sentence that agrees with you, skip the next one which dissagrees with you, and then bold a chunk about end-of-life because...

...actually, I've no idea. I thought we were talking about resurfacing - And I note 'Perpetual Pavement' still needs that, which could be done with various form of concrete overlay to improve albedo.

Seriously, why do you feel that paragraph is relevant?

:shrug:

But the language is improved.

[kristopher]

28. Your quote didn't represent the meat of the article

Resurfacing with concrete is much harder than with asphalt because you have to set forms.

Building with asphalt originally allows resurfacing perpetually.

Building with concrete requires complete removal when even asphalt will no longer patch it.

These are the considerations I was referring to. Your reference touches on them, but you focused on a non-disputed issue; whether or not concrete can be used over asphalt. The point I made was that compared to resurfacing with asphalt, to resurface with concrete is more like building the road from scratch - that's the forms, which are required for both new and resurfacing applications.

And you STILL ignore the CO2 emissions from the concrete!!!

[Dead_Parrot]

29. My quote...

..was to counterpoint your statement "Replacing all of that asphalt is an absurd proposition". It very clearly isn't absurd, and if you'd spent 2 minutes on google you'd have found that out for yourself. You don't have to rebuild the road from scratch - whatever it's made of - it can just be layered with concrete and Voilà! Instant albedo.

Costly? Maybe, at least for the first application - the improved wear will off-set that. And with oil around $100/bbl, bitumen isn't getting any cheaper.

More carbon? Possibly, but asphalt is hardly greener-than-green - I'm not going to call that untill I've seen a direct comparison. Post one if you've got it.

"Building with concrete requires complete removal when even asphalt will no longer patch it." is, I suspect, something you've just made up - unless you have a link. The article certainly doesn't say that, it say's "Some pavement types must be completely removed..." Bit of a difference. Unless you are implying they meant to say "All pavement types must be completely removed unless they are Permanent Pavement", but that's a bit of a stretch. But anyway...

..."Building with asphalt originally allows resurfacing perpetually." Yes, if you like. It's only the surface we're worried about.

Absurd? Not a bit of it.

[OneBlueSky]

15. I'm not enough of a scientist to know whether this would work or not . . .

but I DO know that very often the simplest solutions to a problem are the most effective . . .

[Dover]

23. Is a white roof better than an unpainted metal (reflective) roof?

Like a mirror it reflects the sunlight back, but is there something about white that's
better?

[kristopher]

24. Galvanized or stainless

Galvanized I'm sure. I'd say that galvanized is actually gray and less reflective than white or beige metal roofing.

[Fledermaus]

31. I think this will help, ENERGY STAR qualified roof products reflect more of the sun's rays

Why choose ENERGY STAR reflective roofing for your building?
ENERGY STAR qualified roof products reflect more of the sun's rays. This can lower roof surface temperature by up to 100F, decreasing the amount of heat transferred into a building.
ENERGY STAR qualified roof products can help reduce the amount of air conditioning needed in buildings, and can reduce peak cooling demand by 10–15 percent.
During building design and when your existing roof needs replacement are both excellent times to consider reflective roofing. See how much reflective roofing can reduce your building's energy costs

http://www.energystar.gov/index.cfm?c=roof_prods.pr_roof_products

[codjh9]

35. I'd think that would truly make a difference. Can you imagine the ignorant Repubs

making fun of this, though? I guess we'd just have to get some PSA-type commercials done on the subject.

[JohnWxy]

36. very interesting. This would be relatively low cost project, too.